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New "Pomegranate" Design a Fix for Lithium-ion Battery Issues

Scientists at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory believe they have solved key issues associated with silicon anodes, which can be used in lithium-ion batteries.

Anodes, which store energy when a battery is charged, are commonly made of graphite, but it's not the only material that can be used. In fact, a more attractive option is silicon.

That's largely because silicon anodes, which can be used in lithium-ion batteries, as well as lithium-air and lithium-sulfur batteries, can store up to 10 times as much charge as those made out of graphite, Science World Report explains.

However, that's not to say silicon anodes don't have problems. In fact, as Gizmodo's Adam Clark Estes notes, they have two big ones:During charging, silicon swells and, due to its fragility, breaks.Silicon is prone to reacting with batteries' electrolytes, and that can "gunk up the circuits."

Now, scientists at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory believe they have found a solution to those issues. Surprisingly, it looks like it was pomegranates — yes, the fruit — that helped them do so.

The pomegranate solution

In a report published in the journal Nature Nanotechnology, the scientists, led by Yi Cui, an associate professor at Stanford, propose a "hierarchical structured silicon anode ... inspired by the structure of a pomegranate."

The design draws on technology that Cui and his team have been working on for the past eight years, according to a press release put out by SLAC. During that time, they devised a way to encase silicon nanoparticles "that are too small to break into even smaller bits" in carbon "yolk shells." Using silicon nanoparticles that are already as small as they can get addresses the silicon anode breakage problem, while putting those nanoparticles in a carbon shell allows enough room for the swelling silicon undergoes when charging.

More recently, team members Nian Liu, a graduate student, and postdoctoral researcher Zhenda Lu came up with a way to use a microemulsion technique to gather the carbon-encased silicon nanoparticles into clusters and then coat those clusters with "a second, thicker layer of carbon."

The resulting "pomegranate cluster has just one-tenth the surface area of the individual particles inside it," as per the press release. That means a much smaller area is exposed to the electrolyte, cutting any gunk formation down to a manageable level.

Thus far, the design look promising. Lab tests indicate that the pomegranate anodes perform well when made in the thickness needed for commercial battery performance. Further, SLAC quotes Cui as saying, "[e]xperiments showed our pomegranate-inspired anode operates at 97 percent capacity even after 1,000 cycles of charging and discharging, which puts it well within the desired range for commercial operation."

Next steps

In the future, Cui and his team see their pomegranate-inspired design allowing for smaller, lighter rechargeable batteries for electric cars, cell phones and more, states Science World Report.

Don't expect to see such batteries just yet, though — the scientists need to simplify the process and find a cheaper source of silicon nanoparticles before their technology can be considered commercially viable, according to Cui.

That said, Tina Casey of CleanTechnica sees promise in the fact that the team has already been at work on its project for eight years — that, she believes may shorten its path to commercialization. And, she notes, Cui is the founder of lithium-ion battery company Amprius, whose board of directors includes a former US energy secretary and which last month raised $30 million to "commercialize the first-generation version of its silicon based Li-ion batteries."

Securities Disclosure: I, Charlotte McLeod, hold no direct investment interest in any company mentioned in this article.